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Lightening the footprint of commercial vehicles

Load capacity has traditionally been the fi rst concern for designers of light commercial vehicles (LCVs). Today’s criteria include cost, environmental performance, and the fact that LCVs (also known as vans) are now used to transport both goods and people. If the LCV is to be electrically powered or used to transport passengers, a vehicle with higher safety standards is required. Addressing these needs at the lowest possible cost requires modular solutions which can be serially produced to meet demand.

From 2017, makers of N1-type LCVs (see text box) will face fi nancial penalties in the European Union if the emissions of their vehicles exceed 175 grams/kilometre. While this limit will be phased-in from 2014, the 2020 target is just 147 g/km. These targets are pushing van manufacturers to look at a range of solutions from weight reduction to a complete shift towards electric power.

With these considerations in mind, ArcelorMittal’s Automotive Global R&D team set out to create a new underbody platform for both fuel- and electricpowered LCVs. The goal was to develop a single underbody module which can reduce the weight and total cost of ownership of both variants. The underbody was chosen as the first module for optimisation as it is typically similar across different models. Manufacturers often utilise the same underbody for 10 to 12 years, simply modifying the upper structure to create new passenger models or cargo versions with different volumes.

Increased use of high strength steels

A recent-model baseline LCV was selected for the fuel-powered engine study. The reference underbody mainly comprises high strength low alloy (HSLA) steels and had a total mass of 193 kg.

Utilising ultra high strength steels (UHSS) and advanced high strength steels (AHSS) such as Usibor® and Ductibor®, ArcelorMittal’s engineers have been able to reduce the total weight of the underbody to 155 kg, a reduction of 38 kg or 19.8% compared to the baseline model. UHSS and AHSS now represent more than 85% of the underbody module.

What are light commercial vehicles (LCVs)?

Over 85% of the redesigned LCV underbody is comprised of AHHS and UHHS, including PHS (press-hardened steel, Usibor®).

In the EU, LCVs are classed as either M1 or N1 and account for around 12% of the EU market for light-duty vehicles. M1 vans are used to transport passengers and have a maximum of eight seats, not including the driver. N1-type LCVs are designed for the carriage of goods and have an unladen weight less than 3,500 kg.

N1 models fall into one of three main sizes. The smallest can carry around 800 kg of cargo and have a load space of about 3 m3. In the middle, models typically have a capacity of 1,200 kg in a 7 m3 load area. The largest LCVs can carry 2 tonnes of cargo and typically have a volume of 17 m3.

Lower cost and weight, equal safety

ArcelorMittal engineers paid particular attention evaluating the performance of the redesigned underbody in several crash scenarios. Analysis of frontal, rear and lateral crash data for the fuel-powered model has shown it has the equivalent safety performance as the baseline, despite the signifi cant weight reduction.

Although more costly and stronger UHSS and AHSS have been used in the design, overall material costs of the optimised solution are lower. This is because much less material is required to achieve the required performance. Industrial validation is expected to show that further savings can be achieved during manufacturing thanks to process improvements and the use of laser welded blanks (LWBs).

The study has proven that UHSS and AHSS have the potential to lighten LCVs and reduce costs. By utilising them in other parts of LCVs, such as the upper structure, even greater savings should be possible while improving safety.

Electric LCVs

As electric technology matures, more light commercial vehicle (LCV) manufacturers are expected to launch electric-powered vans. Most manufacturers utilise the same underbody for both their electric- and fuel-powered models.

As part of this study, Automotive Global R&D has developed a battery-powered LCV solution. While work on this variant is ongoing, ArcelorMittal’s engineers anticipate a weight reduction of the underbody by around 19%.

The baseline electric vehicle has a payload of 900 kg and a range of 130 km. By reducing the weight of the underbody, vehicle manufacturers can either increase the payload or improve the vehicle’s range.

Signifi cant attention has been paid to the design in order to prevent vehicle parts from penetrating the battery in the event of a crash. The frontal crash management strategy has focussed on the reinforcement of the front side members and the use of laser welded blanks (LWBs) to manage crash energy. As the battery comes close to the edges of the underbody, lateral crash management has been a major consideration. Side sill reinforcement has been added using a lightweight AHSS. UHSS and AHSS have also been used to create a crash box and cross member to absorb energy in the event of an accident.